Portable builder&#39;s hoist



May 29, 1962 M. SAMUELY PORTABLE BUILDER'S HOIST Original Filed April25, 1955 5 Sheet l FIG.|.

FIG.3.

MAX SAMUELY INVENTOR HERZIG a JESSUP,

BY ATTORNEYS.

y 2 M. SAMUELY 3,036,435

I PORTABLE BUILDER'S HOIST Original Filed April 25, 1955 3 Sheets-Sheet2 F l G. 5. F l G. 6. BLOCKED FLOW VALVED CRACKED IIIIIIIII lanmlimnmnwHYD. VALVE HYD. VALVE FU LL FLOW MAX SAMUELY INVENTOR.

HERZIG at JESSUP,

ATTORNEYS.

y 9, 1962 M. SAMUELY 3,036,435

I PORTABLE BUILDER'S HOIST Original Filed April 25, 1955 3 SheetsSheet 5FIG. nQ

MAX SAM UELY IN VEN TOR.

HER-ZlG JESSU P,

ATTO RN EYS.

Unite rates atent O 3,036,435 PORTABLE BUILDERS HOIST Max Samuely, LosAngeles, Calif., assignor to Tubular Structures Corporation of America,Los Angeles, Calif., a corporation of California Original applicationApr. 25, 1955, Ser. No. 503,681, now Patent No. 2,869,325, dated Jan.20, 1959. Divided and this application Jan. 19, 1959, Ser. No. 787,512

12 Claims. (Cl. 60-53) The present invention relates generally tohoisting equipment and elevators and more particularly to a portablehoist adapted for lifting and lowering materials in the course ofconstructing or razing buildings. It will be realized from thedescription to follow that the invention herein described is not limitedto the specific embodiments shown and described, but will haveapplication in other allied fields.

This application is a division of earlier filed application Serial No.503,681, filed April 25, 1955, now Patent No. 2,869,325.

Devices of the type generally described above have been available in thepast but have been subject to a number of disadvantages. Previouslyknown hoists of this general type consist of a tower having verticalguides, a platform engaged with the guides, and a simple winch forraising or lowering the platform along the guides.

Prior to the present invention, portable hoists in general use have notbeen designed for rapid and eflicient use in that they have notincorporated means for accelerating and decelerating the platform travelat the beginning and ends respectively of its movement up and down thetower guides. Because of the lack of such accelerating and deceleratingmeans, the platform movement has been re stricted to relatively slowspeeds since the shock attendant to starting and stopping a platform athigher speed involves the risk of breakage of the winch cable or otherportions of the hoisting mechanism with obvious disastrous results.Furthermore, it is desirable in hoisting plaster, mortar and othermaterials carried in the skips that an operator ride on the platformwith the material so as to be available to stop the platform at thedesired point and roll the skip off the platform at the elevatedstation. Abrupt stopping and starting of the platform involves severediscomfort and danger to personnel riding thereon and thus should beavoided.

Since the shocks above mentioned has been avoided in the past only byslowing down the platform movement, previous hoists have been somewhatineflicient, particularly when used for relatively high lifts in theconstruction of multistory buildings due to the excessive time taken forthe platform to travel from the ground to the desired elevation.

Another difficulty encountered in hoists of the type described whichhave been available heretofore is the fact that the down-travel of theplatform has been controlled solely by a mechanical friction brake whichtends to become overheated upon continued use particularly in demolitionand razing operations wherein the platform is loaded during thedown-travel. Mechanical brakes of the type described have the additionaldisadvantage that they are subject to grabbing or seizure such as toimpose excessive shock loads on the hoisting cable running substantialrisks of breakage.

Still another disadvantage of prior devices is the fact that nosatisfactory means have been provided hereto-fore in hoists of the classdescribed for accurately and automatically positioning the platform at adesired elevated station while at the same time permitting relativelyhigh speed travel during the major portion of the up-travel.

Bearing in mind the foregoing difiiculties, it is a major object of thepresent invention to provide a portable hoist ice of the class describedin which relatively high speeds of up and down travel may be obtainedwithout attendant shocks at the beginning and end of such travel.

It is another object of the present invention to provide portablehoisting equipment of the class described in which the speed of up anddown travel may be adjusted over a relatively wide range for variousapplications.

It is still another object of the invention to provide hoistingequipment of the class described which is capable of accurate andautomatic placement of the hoisting platform at a desired elevatedstation.

It is a further object of the invention to provide equipment of theclass described wherein a high speed of platform travel is combined withan automatic decelerating means which slows the platform down just priorto reaching the desired elevated station.

An additional object of the invention is to provide for fully controlleddown-travel of platform in hoisting equipment of the class describedWithout the use of mechanical friction devices.

Yet another object of the invention is to provide hoisting equipment ofthe class described wherein the speed and operation of the power primemover is automatically coordinated with motion of the platform.

Yet a further object of the invention is to provide an automatic safetybrake system for stopping the downtravel of the platform in the event offailure of the speed control equipment.

Another object is to provide improved and simplified hydraulic circuitryin a hydraulic hoist wherein the hoist drives a motor-pump unit actingas a pump during down movement.

Another object is to provide an improvement as in the foregoing whereinautomatic flow restrictors are provided in the hydraulic connection tothe motor-pump unit so as to control the up and down travel of thehoist.

Another object is to provide in the system an internal compositionprime-mover controlled by a hydraulic throttle and a hydraulic brakehaving simplified hydraulic circuitry for providing automatic actuationof the throttle and brake.

The foregoing and additional objects and advantages of the inventionwill be apparent from the detailed description to follow, considerationbeing given to the ac companying drawings in which:

FIG. 1 is an elevational view of a portable builders hoist embodying thepresent invention, the same being shown in a. lowered or travelingposition;

FIG. 2 is a fragmentary side elevational view of the hoist shown in FIG.1 in erected positions ready for operation;

FIG. 2a is an enlarged horizontal section taken on the line 2a-2a ofFIG. 2;

FIG. 3 is a fragmentary elevational view partially sec, tioned, showinga first form of hydraulic control valve and operating cam embodied inthe hoist shown in FIGS. 1 and 2;

FIG. 4 is an elevational section taken on the line 44 in FIG. 3;

FIGS. 5, 6, and 7 are sequential semi-schematic views of a second formof hydraulic control valve and operating cam which may be embodied inthe hoisting equipment shown in FIGS. 1 and 2;

FIG. 8 is an axial section of a uni-directional, constant flow regulatorincorporated in various of the control systems embodied in the presentinvention;

FIGS. 9, 10 and 11 are hydraulic circuit diagrams schematicallyillustrating the operation of certain forms of the invention during theup-travel, stop, and downtravel conditions respectively;

FIGS. 12 and 13 are fragmentary semi-schematic views of aprime moverthrottle control portion of the system shown in FIGS. through 12 showingrespectively, open and closed throttle positions.

The portable builders hoist embodying the present invention is indicated'in'the drawings generally by the reference character and comprises aframe-work tower 31 having longitudinal guide rails 32 on a forward facethereof, a load carrying platform33 mounted for sliding movement alongthe rails 32 and a draw works 34 incorporating a winch drum 35 having ahoisting cable 36 reeved through conventional sheave means showngenerally at 37 whereby to hoist or lower the platform 33. The hoist 36includes a base frame 40 having suitable ground engaging pads 41 and 42,the entire structure being mounted on a pair of trailer wheels 43whereby the hoist 30 may be drawn behind a towing vehicle being attachedby conventional trailer attachment means (not shown) at the upperend 44of the tower 31.

When it is desired to lower the tower 31 from the operative positionshown in FIG. 2 to the traveling position shown in FIG. 1 the rearmostground engaging pads 42 are retracted lowering the wheels 43 to theground and the tower 31 is thereafter tilted rearwardly(counterclockwise in FIG. 2) about a horizontal pivot axis at 45 untilthe tower rests against abutments 46 connected to the carriage (notshown) supporting the wheels 43.

Power to operate the hoist 30 is derived from a prime mover 50, inthepresent case an internal combustion engine. As may be seen in FIGS. 9through 11, the prime mover 50 is mechanically connected to drive ahydraulic pump 51 which may be any type of relatively high pressure pumppreferably of the positive displacement type such as a gear pump, vanepump or the like. The pump 51 derives its fluidfrom a storage tank 52and delivers it through control means to be determined in more detaillater herein to a hydraulic motor 53 which is again preferably of thepositive displacement type. The hydraulicmotor53 is mechanicallyconnected todrive to unwind from the drum 35 and this unwinding rotationof the drum 35 in turn driving the motor 53 backwardly causing the sameto pump fluid. The speed of the down travel of the platform 33 maytherefore be controlled by restricting the flow from the hydraulic motor53 (now acting as a pump).

Restriction to flow from the hydraulic motor 53 during the down-travelof the platform 33 is effected by an adjustable flow regulator 63 (seeFIGS. 9-11) which in the first form of invention takes the form of auni-directional flow regulator, the construction of which is shown inFIG. 8. In the device shown in FIG. 8 flow regulation takes place onlywhen the flow is from the motor 53, i.e., through the device in adirection entering at the conduit 69 and leaving at the conduit 70. Thisflow direction is indicated by the arrow in the conduit 69 in FIG. 8 andit will be seen that as the fluid passes in this direction into achamber 71 in the regulator 63 a restricted orifice 72 in a slideablepiston valve member 73 therein, causes pressureto build up in thechamber 71 urging the piston 73 to the left against the yieldingresistance of a spring 74. The resistance of the spring 74 may beadjusted by an abutment screw 75 by which the initial stress on thespring 74 may be varied. As the piston 73 moves to the left, the skirtthereof passes across an exit port 77 leading to the conduit wand thuscauses an additional restriction to flow through the entire regulator68. For any given pressure, the increased restriction at the port 77decreases the winch drum 35 to wind the cable 36 thereon and lift theplatform 33.

A spring-held pressure suspended friction brake 55 is operativelyassociated with the winch drum 35 and fluidconnected to the hydraulicsystem whereby the drum 35.

is held stationary by a brake shoe 56 forced into contact therewith bythe compression spring 5 7 except where there is operative hydraulicpressure in a high pressure conduit 58 as will be described. Pressure inthe conduit 58 forces fluid into the upper end of an actuating cylinder59 causing a piston 60 to draw downwardly on the brake shoe 56 releasingthe same from the 'drurn35 and permitting the latter to rotate. Thecompressive force 'of the spring 57 is Is'ufiicient to hold the drum 35stationary with the platform 33 in a raised position and with themaximum permissible load thereon. The brake 55 is used only to lock theplatform in a desired position and is not'used to slow the down-travelof the platform 33; 'Other means are provided for the latter purpose ass will be explained.

The hydraulic pressure system also includes a conduit 62 leading to anactuating cylinder 63 having a piston 64 therein mechanically connectedto a throttle lever- 65 which controls the speed of the prime mover 50.A compression spring 66' normally urges the throttle lever 65 upwardly,iJe. in a closed throttle direction... The open throttle and closedfthrottle conditions are illustrated in FIGS." .12 and 1-3 respectively.From the foregoing it 50 and the same idles. When pressurized fluid isintroduced through'the conduit 62 into the actuating cylinder 63,however, the piston 64 moves downwardly opening the throttleand speedingup the operation of the prime mover 50 thus increasing the powerdelivered to the pump 51.

the rate of flow through the regulator 68. As such flow must all passthrough the orifice 72 the decrease in rate of flow decreases thepressure in the chamber 71 thus permitting the spring 74 to move thepiston 73 to the right tending to open the port 77. When these twoopposing forces reach a condition of equilibrium the rate of fluid flowthrough the regulator 68 reaches a certain relatively constant value andit will be seen that this value is substantially the same irrespectiveof the pressure at the con duit 69. 7

Thus the maximum speed at which the motor 53 may be driven by the drum35 during the down-travel of the platform -33 is limited to that whichproduces the limited flow rate through the regulator 68.

In order to prevent damage to the pump 51 or the hydraulic'motor 53 inthe event of a malfunction in the control system causing abnormal flowthrough these devices, each is connected by a high pressure relief valveto the storage tank 52. The high pressure relief valve for the pump 51is indicated in the drawings at. 80 and that for the hydraulic motor 53is indicated at 81;

As thus far described, it will be seen that the control of the platform'33 whereby it is caused to move upwardly or downwardly as desired isaccomplished by connecting the pump 51 to deliver pressure to thehydraulic motor on the one hand or alternatively connecting the outputof the motor 53 to the tank 52 through the flow regulator 68 in suchmanner as to restrict the fluid flowing from the hydraulic motor 53.These selective connections are accomplished by means of a mastercontrol valve 85 which in the form illustrated in FIG. 3, is a four-waythree position spool valve.

The internal construction of the'valve 85 is more or less conventionaland is illustrated in FIG. 3 wherein it will be seen that pressure fluidintroduced at a conduit 86 will be seen that when there-is no pressureinthe conduit .62 the spring 66 closes the throttle of the primemovermay be selectively connected through internal passages in the valveto a tank connection conduit 87; a motor connection conduit 70, or analternate return conduit 88. Selective inter-connection as justdescribed is accornplished by moving a spool member 89 axially withinthe body of the .valve 85 in one direction or the other from a centralposition inwhich itis held bya centering spring assembly illustrated at99;

' Inasmuch as the specific details of the four-way valve employed in thepresent invention are conventional and inasmuch as the inventiondoes'not' reside in the particular design of the valve itself, nofurther detailed description is deemed necessary herein. Sufiice it tosay, that when the spool 89 is moved to its right-hand limiting position(e.g. FIG. 9) pressure fluid from the conduit 86 is connected to theconduit 70. When the spool 89 is centered (e.g. FIG. 10) fluid from theconduit 86 may flow unrestricted through conduit *87 to the tank 52.

Interposed in the return conduit 88 between the control valve 85 and thetank 52, is a flow restriction valve relief 95, the purpose of which isto maintain some pressure in the conduit 58 even when the valve is inposition to return pressure fluid through the conduit 83 to the tank 52.This pressure in the system is required during downtravel as can be seenin FIG. 11, in order to hold the brake-shoe 56 away from the drum 35 andpermit downtravel of the platform 33 and also to maintain pressure inthe conduit 62 so as to open the throttle of the prime mover 50sufiiciently to produce the pressure necessary to hold the brake off.

At this point it should be noted that the system fails safe that is, inthe event of a failure of the prime mover or any part of the hydraulicsystem, pressure is released from the brake actuating cylinder 59 ornever builds up therein, thus keeping the brake on and preventingoperation of the system until the failure is corrected.

Movement of the spool 89' back and forth from its spring centeredposition in the body of the valve 85 is effected by a rotary cam systemmounted on a shaft 96 and adapted to engage one or the other of two camfollower rollers 97 and 98 which are in turn mounted on a common slidemember 99 connected through a connecting rod 100 to the spool 89.

In one form of the device illustrated in full line in FIG. 3, afinger-like cam 101 (shown in full line in FIGS. 9-11) is employed,having a relatively restricted cam surface 102 adapted to contact therollers 97 and 98 only at, or near the ends of its 180 rotary movement.In this form, a dash-pot 102 is operatively associated with theconnecting rod 100 whereby to damp the motion of the spool 89 returningto its center position from either of its left-hand or right-handlimited positions. That is, assuming the cam 101 to have been rotated toits lirni-ting position clockwise thus contacting the cam followerroller 98 and moving the spool 89 to its extreme righthand position andassuming that the cam 101 is thereafter rotated to a centralizedposition as illustrated in full line in FIG. 3, the spool 89 will returnto its central position under the urging of the centering springassembly 90. The spool will however return somewhat slowly due to thedamping action of the dash-pot 102 wherein a piston 103 causes fluid onone side thereof to pass through a restrictive orifice 104 and a passage105 to the other side of the piston 103. The restriction of the orifice104 may be adjusted by a needle valve 106. The purpose of thisarrangement will be described later herein,

As can be seen in FIG. 2, the cam shaft 96 is mounted on a common basewith the winch-drum 35 and prime mover 50 is drivingly connected throughsprocket chains 110 and 111 to a control cable drum 112. Two sprocketchains 110 and 111 are employed and engage separate sprockets on acommon shaft coaxial with the Pivot axis at 45 whereby the raising andlowering of the tower 31 does not interfere with or disturb the drivingconnection between the cam shaft and the cable control drum 112.

Provision for manual, as well as automatic operation of the mastercontrol valve 85 is made in the form of a control cable 115 mounted on apair of drums or pulleys the lower one of which is the control drum 112and the upper of which, indicated at 116, is mounted at the upper end ofthe tower 31 whereby to provide a length of control cable at 117 whichis parallel to and closely adjacent the platform guides 32.

Clamped to the cable 115 at appropriate points along the length 117 aretwo stop members 118 and 119 conventionally referred to as eggs. As canbe seen in FIG. 2 the platform 33 is provided at its rearward edge witha pair of vertically extending slide members 120 adapted to engage theguides 32. At the upper end of one of the slide members 120 is a closedfork 121 which is positioned to bracket the cable length 117 as can beseen in FIG. 2A.

It will be seen that as the platform 33 reaches either its upper orlower limiting position in its travel along the tower 31, the fork 121engages one of the other of the eggs 18 and one 19, thus moving thecable 115 and rotating the control drum 112. The rotary motion of thecontrol drum 112 is transmitted through the previously describedsprocket chain connection and cam to the valve spool 89 thus changingthe position thereof. The just described control cable-sprocket chainconnection to operate the valves is common to all of the inventionillustrated herein.

As has been previously described the normal position of the valve spool89, when not influenced by the cam 101, is in the center of its movementin the body of the valve 85. When in this position as shown in full linein FIG. 3 and as is indicated schematically in FIG. 10, pressure fluidentering at 86 is transmitted directly through the valve withoutsubstantial resistance and returned to the tank 52 through returnconduit 87. Since there is no resistance to the flow of fluid in themanner just described substantially no pressure is developed in theconduit 58 and thus the brake shoe 56 remains against the drum 35 andthe throttle 65 remains in idling position.

The normal or non-operating position of the cam 101 is shown in fullline in FIG. 3 wherein it will be seen that the cam is midway betweenthe cam follower 97 and 98 and out of contact with the same.

Operation Assuming that the platform is resting on the ground, has beenloaded, and it is now desired to raise the same; the operator pullsdownwardlyon the cable length 117 (this motion is possible since thelower egg 118 is below the fork 121). Downward movement of the cablelength 117 rotates the control drum 112, and hence the cam shaft 96 in aclockwise direction thus bringing the cam surface 102 against the camfollower 98 and moving the valve spool 89 to its right hand limitingposition. This condition is illustrated in FIG. 9 wherein it will beseen that the valve is placed in a position to intercommunicate thepressure conduit 86 with the outlet conduit 70 which communicatesthrough the flow regulator 68 with the hydraulic motor 53. It will benoted that in this condition the flow through the regulator 68 is in thereverse direction (as to the regulator) thus forcing the piston 73upwardly and permitting the full flow that can pass through the orifice72. The flow just described delivers pressurized fluid through theconduit 69 to the hydraulic motor 53 whence it is returned through areturn conduit 129 to the tank 52. This in turn causes powered rotationof the drum 35 in a direction to lift the platform 33 as previouslydescribed.

It will be noted that the pressure in the conduit 58 lifts the brakeshoe 56 from the drum 35 and also, through the conduit 62, operates theactuating cylinder 63 to open the throttle 65. It will also be notedthat should the hydraulic system fail at any time the pressure in theconduit 58 would drop permitting the spring 57 to engage the brake 55and hold the platform 33 at its then position along the guides 32.Similarly, such a failure would close the throttle on the prime mover 50and prevent the same from running away due to a no-load condition.

Returning now to the operation of the platform 33 in an upwarddirection, let it now be assumed that the fork 121 reaches the upper egg119 thus rotating the control drum 112 in a counter-clockwise directionand moving the cam 101 from its position against the cam follower 98 toits vertical disengaged position illustrated in FIGS. 3 and 10.Referring to the form of the invention illustrated in FIG. 3 it will berealized that the return of the valve 7 spool 89 to a centralizedposition under the urging of the spring assembly 90 will be damped orslowed down by the dash-pot mechanism 102 due to the fact that liquidmust be forced from the left-hand side of the piston 103 through therestricted orifice 105 to the right-hand side of the piston 103. Thejust described damped movement of the valve spool 89 gradually cuts offthe communication between the pressure conduit 86 and the output conduit70 so that the fluid delivered to the hydraulic motor 53 is cut offgradually rather than abruptly. It has been found that if the cut-oif isgradual over a period as short as one second or even less, the shockupon stopping the platform is substantially eliminated. On the otherhand,

if the valve spool were permitted to snap back to central position underthe sole control of the spring assembly 90 the stoppage of the platform33 is not only unduly abrupt but the shock in the hydraulic fluid systemis also severe.

in addition to preventing the sudden stoppage of the platform 33, itwill be seen that the dash-pot 102 imposes a yielding resistance tomovement of the spool 89 to either of its left-hand or right-handpositions at the time that the cam 101 is manually moved into engagementwith the followers 97 or 98. Thus, the operator is prevented frominadvertently jamming the valve 85 into 'full speed condition, imposingan undue starting load on the device. r

In addition to the automatic stopping at the'contact of the fork withthe upper egg.119, platform 33 may of course be stopped at any desiredposition by an operator on the ground lifting on the cable length 117.Also, an

operator riding on the platform 33 can, in the usual manner, stop theplatform at any desired point by seizing the cable length 117 andlifting the same or permitting the I is rotated counter-clockwise to theleft-hand position against the cam follower 97 moving the valve spool 89to its left-hand position and intercommunicating the conduit 70leadingfrom the hydraulic motor 53 with the return conduit 87 connectedto the tank 52. At'the same time, the pressure conduit 86 'is connectedas shown in FIG. 11, to the output conduit 88 and fluid is deliveredthrough the restrictive valve 95 to the tank 52. The pressure built upin the conduit 58 by-reason of the restriction imposed at the valve 95is sufficient to release the brake 55 and also to open the throttle 65through the fluid actuated devices 59 and63 previously described.

The brake 55 having been released, the weight of the platform 33 and anyload thereon causes the cable 36"to unwind from the drum 35 which nowdrives the hydraulic motor causing the same to operate as a pump. Themotor 53 then receives fluid through the conduit 12.9 from the tank 52and' pumps the same through the regulator 68, the conduit70, the valve85, and the return conduit 87'back to the tank 52. The flow rate throughflie regulator 68 maybe adjusted by means of the adjustmerit screw 75 aspreviously described, and is adjusted to give the desired rate ofdownward travel of the platform. It will be noted that this downwardtravel rate is substantially uniform and remains approximately the sameirrespective of the load on the platform 33 since the rate ofdown-travel is directly proportional to the rate of fluid of theeffective cam surfacefdwell portions 133and 134' adjacent the riseportions 131 and 132 and a central high dwell at 135. In this form ofcam controlno dash-pot is required, the desired graduated operationbeing accomplished by the cam alone.

The respective positions of the cam 13!) and the valve spool 89 duringstopping and starting are shown in FIGS. 5, 6, and 7. It will be seenthat when the cam 130 is rotated for example clockwise to engage thefollower roller 98, its first contact moves the spool 89 out of itscentralized position and for a short time, blocks all flow through thevalve 85. The result of this is to quickly build up pressure in theconduit 58, thus releasing the brake 55 and opening the throttle 65 inthe manner previously described. The next successive position of the cam130 and valve spool 89 is illustrated in FIG. 6 wherein it will be seenthat upon reaching the dwell 134, for example, the valve 85 is slightlycracked whereby to permit a highly restricted flow of fluidtherethrough. The effect of this is to slowly start the motor 53 (eitherupwar-dly tor downwardly depending on the left-hand or right-handposition of the spool 89) thus preventing an abrupt start. Such slowspeed (about /2 normal speed) 7 continues as long as the cam follower 97or 98 is engaged with the dwell 133 or 134.

When'the cam 130 is now rotated to its limit in either the right-hand orleft-hand position, the engaged follower 97 or .98 is lifted onto thehigh dwell portion 135 whereupon the valve spool 89 is moved to the fullopen position as illustrated in FIG. 7 causing the platform 33 to moveat full speed.

While the forms of the device shown and described herein are fullycapable of achieving the objects and providing the advantageshereinbefore stated it -will be realized that they are capable ofconsiderable modification and rearrangement Without departure from thespirit of the invention. For this reason, I do not mean to be limited tothe forms shown and described but rather to the scope of the appendedclaims.

What is claimed is:

1. In a hoist'of the type having a load such as a carrier to be liftedor lowered, a hydraulic motor for lifting said load which motor acts asa pump upon lowering of the load, a hydraulic system including a tank, apump having an outlet and valve means for reversing the flow ofhydraulic fluid through the motor, the improvements comprising: meansincorporated in said valve means for freely bypassing fluid from theoutlet of the pump through a first passage to the tank when the valve isin load stopping position, said valve means having a down positionwherein hydraulic 'tluid from the motor is returned to the tank througha second passage having flow restricting means therein whereby pressureis maintained in the outlet of said pump, and means responsive tosaidpressure for controlling the functioning of portions of said hoist.

2. The structure of claim 1 wherein said last-named means comprises ahydraulic brake of the type having means which are released upon theapplication of hydraulic pressure thereto, said brake having a directconnection to the outlet of said pump so that the said brake is releasedwhenever there is pressure in said pump outlet.

3. The structure of claim 1 including a prime mover for driving saidpump, saidprime mover having a hydraulic throttle of a type which opensupon the application of pressure thereto and having a direct connectionto the outlet of said pump so that said throttle is opened whenevertheoutlet of said pump is not freely bypassed to the tank, 7 j

4. The structure of claim 3' including a hydraulic brake of the typehaving means which are released upon the ing an intermediate positionand an up position and cam means for actuating said valve means from itsintermediate position to either the up or down position.

6. The structure of claim wherein said cam means includes a cam having aconfiguration providing for variable degree of opening of the ports insaid valve means.

7. In a power hoisting system a hydraulic transmission comprising: asource of pressurized fluid; a reservoir; a hydraulic motor-pump havinga port and being connected to drive as a motor when supplied withpressurized fluid at said port and to deliver pressurized fluid at saidport when mechanically driven as a pump; conduit means connected betweensaid source of pressurized fluid, reservoir and said port to saidmotor-pump; valve means interposed in said conduit means having an upposition in which the source of pressurized fluid is connected with saidport and a down position in which said port of said motor-pump isconnected to said reservoir and automatic flow regulator means connectedto restrict flow from said motor-pump to regulate its rate of operationwhen acting as a pump.

8. The structure of claim 7 wherein said flow regulator is of a typewhich provides for relatively unrestricted flow in the reverse directionso 'as to allow relatively free Iflow of hydraulic fluid to saidmotor-pump when acting as a motor.

9. The structure of claim 7 including a hydraulically operated brake andbrake motor associated with said hoi said brake being of a type arrangedto release upon the application of hydraulic pressure to said brakemotor, means providing a direct connection from said source ofpressurized fluid to said hydraulic brake motor, and flow restrictingmeans providing for restricting the output of said pump in both the upand down positions of said valve means whereby suflicient pressure isdeveloped in said connection to actuate said brake motor.

10. The structure of claim 7 including a prime mover connected to saidsource of pressurized fluid, said prime mover having a hydraulicallyoperated throttle having a connection to said source of pressurizedfluid whereby said throttle is moved whenever the output of said sourceof pressurized fluid is restricted so as to increase the pressure insaid connection.

11. The structure of claim 9 including a first unrestricted bypasspassageway from said valve means to said reservoir and a secondrestricted passageway from said valve means to said reservoir, saidvalve means including means whereby said restricted passageway is openfor communication with said valve means in the down position of saidvalve means.

12. The structure of claim 9 including a uni-directional flow regulatorconnected between said valve means and said motor-pump adapted to offerrestriction to flow from said motor-pump but to allow free flow ofhydraulic fluid thereto.

References Cited in the file of this patent UNITED STATES PATENTS1,259,090 Ferris et al. Mar. 12, 1918 2,316,926 Willett Apr. 20, 19432,321,880 Vickers June 15, 1943 2,399,685 McCoy May 7, 1946 2,407,692Vickers Sept. 17, 1946 2,416,801 Robinson Mar. 4, 1947 2,545,440 BarberMar. 20, 1951 2,599,052 Forman June 3, 1952 2,681,117 Marcy June 15,1954 2,789,542 Vander Kay Apr. 23, 1957 2,869,325 Samuely Ian. 20, 1959

